Waste material that accumulates in landfills is collected in an area until it reaches a certain depth, and is then covered by a thin layer of soil. This process is repeated until the depth of the waste material or soil layers reach several hundred feet, and then the landfill is covered by a final layer of soil. Much of the waste material is composed of biodegradable materials, and the decomposition of these materials in the landfill environment produces methane and other flammable gases, often deep underground. If these gases are not collected and treated, they may leak to the surface, causing air pollution and becoming a flammability hazard for vehicles. Further, similar gases may diffuse horizontally through the soil, resulting in these hazards far from the landfill itself.
To combat these hazards, wells are often constructed to collect and transport the methane and other gases to a facility where they can be disposed of safely. Typically, a hole is drilled into the landfill to where the gases are generated. Pipe sections, normally made of polyethylene, which is resistant to the corrosive environment of the landfill, but occasionally made of other materials such as carbon steel or PVC, are lowered into the hole to provide a conduit for the escaping gases. These sections are joined to create a continuous conduit to the surface of the landfill. The piping is perforated at the lower end to allow the gases to reach the interior of the piping, and the upper portion of the piping is solid in order to provide a continuous conduit. The top of the piping extends a few feet beyond the surface of the landfill, and is connected to a vacuum system used to pull the gases upward from their point of generation through the use of flexible or fixed piping. This extension of the well beyond the surface of the landfill is termed a wellhead pipe. In some known wellhead assemblies, the connection from the vacuum system to the wellhead pipe is made using a flanged connection. In other known wellhead assemblies, the connection is made by a pipe member or the like that fits over the wellhead pipe and is permanently secured by glue or another bonding material to the wellhead pipe to prevent any gas from escaping. There may be as many as two hundred or more of these wells and connections in a large landfill. Each of the known wellhead assemblies involves securing the wellhead assembly to the wellhead pipe in a manner that renders it extremely difficult or impossible to subsequently remove. As will be described in further detail below, this inherent feature of known wellhead assemblies is quite problematic, because wellhead assemblies must frequently be removed from their corresponding wellhead pipes.
Because of the decomposition of the biodegradable materials and the natural settling processes in the landfill, the surface of the landfill may be reduced in elevation by many feet over time. As a result of this settling, the polyethylene piping that previously extended merely a few feet above the surface may eventually extend many feet beyond that. The flexible connection is then difficult to service and inflexible piping may be strained. The operator of the landfill must then cut the wellhead pipe, and reattach a wellhead assembly to the newly cut wellhead pipe. For wellhead assemblies that are connected via a flange, it is a difficult and laborious process to first remove the wellhead assembly from the old flange, and then weld a new flange onto the newly cut wellhead pipe and reconnect the wellhead assembly. Further, for wellhead assemblies that are permanently affixed to a wellhead pipe, such as by gluing or the like, it is extremely difficult to reuse the wellhead assembly. At the very least, the wellhead piping must be cut to the newly desired height, the new wellhead assembly installed, and then the wellhead assembly glued to the wellhead piping. This process may take several hours, and must be done by specially trained personnel who are exposed to the hazards of the escaping gases for that time.
This difficulty presents serious problems since, once installed, wellhead assemblies must routinely be removed in order to service the landfill wells. For example, it is often necessary to periodically check the pressure differential in the well. This is typically accomplished by removing the wellhead assembly, inserting an orifice plate within the upper end of the wellhead pipe, replacing the wellhead assembly, and measuring the pressure at a point below the orifice plate and at a point above the orifice plate. As indicated, for known wellhead assemblies that are welded, bolted or glued to the wellhead pipe, this is a difficult and time consuming procedure. For such known wellhead assemblies, any other type of maintenance or servicing that requires removal of the wellhead assembly, such as pumping out a flooded well, will likewise be difficult and time consuming.